In general, the present invention relates to telemetry using sensing elements remotely located from associated pick-up and processing units for the sensing and monitoring of pressure within an environment. More particularly, the invention relates to a unique remote pressure sensing apparatus that incorporates a magnetostrictive element (whether hermetically-sealed within a receptacle) and associated new method of sensing pressure of a fluid environment whether under vacuum or in a liquid, gas, or plasma state. Any of a number of applications is contemplated hereby, for example: biomedical applications (whether in vivo or in vitro) including medical test samples, food quality/inspection, monitoring of water (groundwater, treated water, or wastewater flowing in natural waterways, canals, or pipes), and monitoring manufacturing waste, etc. The new pressure sensing apparatus and method(s) provide information by utilizing, or listening for, the magneto-elastic emissions of one or more magnetostrictive elements (whether the element(s) also has a pre-formed region of xe2x80x98localxe2x80x99 hardening). The magneto-elastic listening frequencies of greatest interest are those at the magnetostrictive element""s fundamental or harmonic resonant frequency. The pressure sensing apparatus of the invention can operate within a wide range of environments for remote one-time, random, periodic, or continuous/on-going monitoring of a particular fluid environment.
Pressure sensing can be performed according to the invention without requiring sophisticated equipment and the pressure sensor can be installed/positioned and removed with relative ease and without substantial disruption of the test environment. If need be, the sensor may be fabricated as a micro-circuit for use in vitro, in vivo, within small-sized sealed packaging or medical test samples (e.g., a test tube), and so on. As a micro-element, the invention can be used where space is limited and/or it is desired that the tiny sensor be positioned further into the interior of the sample or environment being tested/monitored. And, whether or not built on a larger scale, the novel pressure sensor can be used within buildings, an aircraft, or other open space. As it is well known, pressure, p, of a fluid (whether in liquid, gas, or plasma-form) is a function of the fluid""s temperature: The instant invention further includes unique features that can sense and accommodate for environment temperature changes to give accurate pressure readings.
The assignee hereof filed pending patent applications (1) U.S. Ser. No. 09/223,689 on behalf of applicants common to the instant patent application, on Dec. 30, 1998 entitled xe2x80x9cRemote Magneto-elastic Analyte, Viscosity and Temperature Sensing Apparatus and Associated Methods of Sensingxe2x80x9d; and (2) U.S. Ser. No. 09/322,403 on behalf of an applicant common to the instant application, on May 28, 1999 entitled xe2x80x9cRemote Resonant-Circuit Analyte Sensing Apparatus with Sensing Structure and Associated Method of Sensingxe2x80x9d. The invention disclosed in the instant patent application and the inventions disclosed in the pending patent applications U.S. Ser. Nos. 09/223,689 and 09/322,403 were invented by applicants who, at the time of invention, were employed by the assignee hereof.
Simply defined, xe2x80x9cmagnetostrictionxe2x80x9d is the phenomena whereby a material will change shape (dimensions) in the presence of an external magnetic field. This effect is brought about by the reordering of the magnetic dipoles within the material. Since the atoms in a magnetostrictive material are not, for all practical purposes, perfectly spherical (they""re shaped more like tiny ellipsoids) the reordering of the dipoles causes an elongation (or contraction depending on the mode of reorientation) of the lattice which leads to a macroscopic shape change in the material. There is a xe2x80x9creverse magnetostrictive effectxe2x80x9d, called the Villari effect: When an external stress is applied to a magnetostrictive material, a strain develops within the material which induces a surrounding magnetic field. Known magnetostrictive materials include alloys of iron (Fe), cobalt (Co), yttrium (Y), gadolinium (Gd), terbium (TB), dysprosium (Dy), and so on.
The so-called magnetoelastic effect is a phenomenon exhibited by ferromagnetic substances. It refers to the interdependence of the state of magnetization and the amount of mechanical strain present in the material and manifests as magnetostriction, volume change upon magnetization and, inversely, change in the state of magnetization upon application of stress. When a sample of magnetostrictive material is subjected to an applied small time-varying (AC) magnetic field superimposed on a much larger direct-current (DC) magnetic field, the magnetic energy is translated into elastic energy and the sample starts vibrating. The mechanical vibrations are most pronounced as the frequency of the applied AC field gets closer to the characteristic resonant frequency f0 of the magnetostrictive sample and a voltage peak for emissions radiating from the sample can be registered by a pick-up coil in proximity thereto. This pronounced conversion from magnetic to elastic energy holds true at harmonics of resonant frequency f0 This condition is known as magnetoelastic resonance. One example of magnetostriction is the xe2x80x9ctransformer humxe2x80x9d we hear when a transformer core xe2x80x9cpulsatesxe2x80x9d upon the application of a 60 Hz magnetic fieldxe2x80x94the xe2x80x98humxe2x80x99 is the emission of acoustic energy that generates sound.
It is well known that electric and magnetic fields are fundamentally fields of force that originate from electric charges. Whether a force field may be termed electric, magnetic, or electromagnetic (EM) hinges on the motional state of the electric charges relative to the point at which field observations are made. Electric charges at rest relative to an observation point give rise to an electrostatic (time-independent) field there. The relative motion of the charges provides an additional force field called magnetic. That added field is magnetostatic if the charges are moving at constant velocities relative to the observation point. Accelerated motions, on the other hand, produce both time-varying electric and magnetic fields, or electromagnetic fields. See Engineering Electromagnetic Fields and Waves, Carl T. A. Johnk, John Wiley and Sons, 2nd Edition (1988). As stated, exposure of a time-varying (sinusoidal/AC) magnetic field will induce a time-varying current in a ferromagnetic sample such that it will emit EM energy. Also, this same piece of ferromagnetic material will emit acoustic and thermal energy due to the changes in size and viscous flexing of the material. An acoustic wave is an elastic, nonelectromagnetic wave with a frequency that may extend into the gigahertz (GHz) range. Acoustic transmission is that transfer of energy in the form of regular mechanical vibration through a medium (as a stress-wave emission). As defined, an ultrasonic wave is an acoustic emission having a frequency generally above 20 KHz (just above human hearing).
The commercially available xe2x80x98anti-theft markersxe2x80x99 (also called electronic article surveillance, or EAS, tags) operate by xe2x80x9clisteningxe2x80x9d for acoustic energy emitted in response to an interrogating ac magnetic field, to sense the presence of an EAS marker. Sensormatic, Inc. distributes an EAS tag (dimensions 3.8 cmxc3x971.25 cmxc3x970.04 mm) designed to operate at a fixed frequency of 58 kHz (well beyond the audible range of human hearing). These EAS tags are embedded/incorporated into articles for retail sale. Upon exiting a store, a customer walks through a pair of field coils emitting a 58 kHz magnetic field. If an activated EAS tag is in an article being carried by the customer, the tag will likewise emit a 58 kHz electromagnetic signal that can be detected using a pickup coil, which in turn may set off an audible or visual alarm. More-recently, these tags are being placed in a box-resonator, sized slightly larger than the tag, such as the tags placed within a cavity 20 of a housing (FIG. 2, US patent Winkler et al.).
Although magnetostrictive ribbons made of magnetically soft amorphous metallic alloys (such as metallic glasses) have been used in a variety of applications such as anti-theft markers, strain sensors and position sensors, magnetostrictive elements have not been utilized as described herein (where the frequency response of the element is of particular significance) to measure pressure. Instead, known pressure sensing technologies generally require the operation of pressure gauges, most of which either operate on the principle of manometry (using a U-tube/differential manometer, or the simple manometer/piezometer which is impractical for measuring the pressure of gases) or utilize the flexing of an elastic diaphragm (the deflection of which is directly proportional to the applied pressure), or utilize the flexing of an arched tube of relatively small diameter such as is the Bourdon-tube gage does. For reference, the pressure in a vacuum (which, like xe2x80x98outer spacexe2x80x99, is virtually void of gases) is called absolute zero, and all pressures referenced with respect to this zero pressure are termed xe2x80x9cabsolute pressuresxe2x80x9d. Thus, atmospheric absolute pressure at sea level on a particular day might be measured at roughly 101 kN/m2 (equivalent to 760 mm of deflection on a mercury barometer). Unlike conventional pressure measurement instruments, the instant invention needs no physical connections, such as wires or cables, to obtain a pressure measurement. No currently-available instrument or gage takes advantage of the magneto-elastic emission properties of magnetostrictive materials to obtain a pressure measurement.
Therefore, a versatile sensor apparatus and method are needed for making pressure measurements within a variety of diverse environments through remote query, without direct electrical hard-wire connection and without the need to specifically orient the sensor element in order to make such measurements. Without reasonable, cost-effective solutions at hand for reliably monitoring pressure environments that are difficult to access, in a timely manner, one cannot obtain important, accurate pressure data; and under certain circumstances it is imperative that reliable comprehensive data be available to scientists, health care professionals, process and quality engineers, environmental agencies, etc.
It is a primary object of this invention to provide a pressure sensing apparatus for operative arrangement within an environment that incorporates a sensor with at least one magnetostrictive element (whether the element(s) has one or more pre-formed regions of xe2x80x98localxe2x80x99 hardening) that will vibrate in response to a time-varying magnetic field (whether radiated continuously over an interval of time or transmitted as a pulse). The magnetostrictive element may be enclosed within a hermetically-sealed receptacle, at least one side of the receptacle having a flexible membrane to which a magnetically hard element is attached. The pressure sensing apparatus also includes a receiver unit capable of picking up emissions (whether EM or acoustic) from the sensor. Preferably, the receiver (a) measures a plurality of successive values for magneto-elastic emission intensity of the sensor taken over an operating range of successive interrogation frequencies to identify a resonant frequency value for the sensor, or (b) detects a transitory time-response of magneto-elastic emission intensity of the sensor due to a time-varying magnetic field pulse to identify a magneto-elastic resonant frequency value thereof. In the latter case, the detection can be done after a threshold amplitude value for the transitory time-response of magneto-elastic emission intensity has been observed; then a Fourier transform can be performed on the transitory time-response of the emission to convert the detected time-response information into the frequency domain.
It is also an object of this invention to provide a method of sensing pressure of an environment using a sensor having at least one magnetostrictive element (whether the element(s) has one or more pre-formed regions of xe2x80x98localxe2x80x99 hardening and is enclosed within a hermetically-sealed receptacle). The method comprises the steps of: operatively arranging the element in the environment in proximity to a DC bias field; applying a time-varying magnetic field or at least one magnetic field pulse (including a series of pulses); measuring a plurality of successive values for magneto-elastic emission intensity of the sensor with a receiver operating over a range of successive interrogation frequencies to identify a magneto-elastic resonant frequency value of the sensor; and using said magneto-elastic resonant frequency value, identify a value for the pressure of the environment. In the event a time-varying magnetic field pulse, or series of pulses, are applied, the method can also include the step of detecting a transitory time-response of magneto-elastic emission intensity of the sensor with a receiver to identify a magneto-elastic resonant frequency value of the sensor to be used for identifying the pressure of the environment. And, to convert the detected time-response information into a frequency domain format, one can perform a Fourier transform on the transitory time-response of magneto-elastic emission intensity detected.
As one can readily appreciate, within the spirit and broad scope of design goals contemplated herein, the innovative pressure sensing apparatus and associated method can be fabricated from micro-components or built on a much larger scale and formed into many different shapes using a variety of suitable materials; and several sensing elements can be incorporated into an array to provide a package of sensing information to accommodate environments at different temperatures. Preferably, each of these additional elements respond to temperature fluctuations at a different rate. One can cross-correlate the responses of the different temperature elements to determine an absolute temperature of the environment which can be used to correct any pressure measurements taken. Furthermore, the simple, yet effective design allows the pressure sensing apparatus and method of the invention to be incorporated into a system that utilizes available computer processors, data acquisition equipment, and memory in the event complex pressure data acquisition and data processing is desired.
The advantages of providing the flexible new pressure sensing apparatus of the invention, and associated new method of sensing pressure of an environment using a sensor with at least one magnetostrictive element, follow:
(a) The invention can be used for one-time (whether disposable), periodic, or random operation, or used for continuous on-going monitoring of pressure changes in a wide variety of environments;
(b) Versatilityxe2x80x94The invention can be used for operation within a wide range of testing environments such as biomedical applications (whether in vivo or in vitro), within medical test samples, food quality/inspection (within or outside of sealed packing), monitoring of contaminants in water (groundwater, treated water, or wastewater flowing in natural waterways, canals, or pipes), monitoring of gas manufacturing waste, etc.;
(c) Simplicity of usexe2x80x94The new sensor structure can be installed/positioned and removed with relative ease and without substantial disruption of a test sample or environment;
(d) Structural design flexibilityxe2x80x94the sensor may be formed into many different shapes and may be fabricated as a micro-circuit for use where space is limited and/or the tiny sensor must be positioned further into the interior of a sample or environment being tested/monitored;
(e) Several sensors may be positioned, each at a different location within a large test environment, to monitor pressure of the different locations, simultaneously or sequentially;
(f) Several sensor elements may be incorporated into an array to provide a package of sensing information about an environment, including pressure and temperature changes;
(g) Receiving unit design flexibilityxe2x80x94One unit may be built with the capacity to receive acoustic emissions (elastic nonelectromagnetic waves that can have a frequency up into the gigahertz, GHz, range) as well as electromagnetic emissions emanating from the sensor, or separate acoustic wave and electromagnetic wave receiving units may be used;
(h) Apparatus design simplicity and associated cost reductionxe2x80x94Reducing the number and size of components required to build a pressure sensing apparatus can reduce overall fabrication costs and add to ease of operation; and
(i) Sensor materials and size can be chosen to make one-time, disposable use economically feasible.
Briefly described, once again, the invention includes a pressure sensing apparatus for operative arrangement within an environment, having: a sensor comprising a hermetically-sealed receptacle, at least one side of which has an flexible membrane to which a magnetically hard element is attached/interconnected. Enclosed within the receptacle is a magnetostrictive element to vibrate in response to a time-varying magnetic field. The apparatus also includes a receiver to measure a plurality of successive values for magneto-elastic emission intensity of the sensor taken over an operating range of successive interrogation frequencies to identify a resonant frequency value for said sensor. Additional further distinguishing features include: (a) the magnetically hard element may be adhered to an inner or outer side of, or embedded within as part of, the membrane; (b) the magnetostrictive element can include one or more of a variety of different pre-formed, hardened regions; (c) the magneto-elastic emission may be a primarily acoustic, if the environment pressure is not under vacuum, or primarily an electromagnetic emissionxe2x80x94the receiver being capable of detecting the primary type emitted; and (d) in the event the time-varying magnetic field is emitted as a single pulse or series of pulses, the receiver unit will detect a transitory time-response of the emission intensity of each pulse (detected after a threshold amplitude value for the transitory time-response is observed) and then convert the time-response information into the frequency domain via Fourier transform.
Further, an elongated magnetostrictive element with at least one pre-formed region need not be enclosed within the hermetically-sealed receptacle if positioned such that it is operational within a DC bias field, which may be generated by a variety of sources. The magnetostrictive element can be ribbon-shaped, a planar-square, plate-shape, and so on, and may be made of an alloy of an element selected from the group consisting of iron, cobalt, nickel, yttrium, gadolinium, terbium, dysprosium, and related metals. The pre-formed region may be made using any of a number of material hardening techniques such as: twisting, creasing, bending/folding, embossing, drawing, punching, hammering, and so on. A pre-correlation made between a series of magneto-elastic resonant frequency values taken for the sensor and a corresponding series of pressure values can be used for the identification of a value for pressure of the environment. A computerized processor can be used for such identification as well as for data acquisition. Additional magnetostrictive elements can be included with the sensing apparatus in an array for use to respond to temperature of the environment. Each element is preferably structured such that it has its own distinct operating range, allowing the receiver to distinguish emissions received from each separate element so that separate types of sensing information can be obtained, tracked and computed. Furthermore, a designated additional magnetizable magnetically hard element which can be activated to support an external stray magnetic field, may be positioned in proximity to the sensing apparatus to act as an ON-OFF switch for the sensor.
Also characterized is a method of sensing pressure of a environment using a sensor with a magnetostrictive element comprising the steps of: providing the magnetostrictive element with a pre-formed region and operatively arranging the element in the environment in proximity to a DC bias field; applying a time-varying magnetic field; measuring a plurality of successive values for magneto-elastic emission intensity of the sensor with a receiver operating over a range of successive interrogation frequencies to identify a magneto-elastic resonant frequency value for the sensor; and using the magneto-elastic resonant frequency value, identify a value for the pressure of the environment.
In addition to the unique features identified above in connection with the apparatus of the invention further distinguishing steps, include: enclosing the magnetostrictive element within a hermetically-sealed receptacle, at least one side of which has an flexible membrane to which a magnetically hard element is attached/interconnected, and operatively arranging the element in the environment; detecting a transitory time-response of magneto-elastic emission intensity of the sensor with a receiver to identify a magneto-elastic resonant frequency value for the sensor (which may be performed after a threshold amplitude value for the time-response of emission is observed); and performing a Fourier transform on the transitory time-response to convert it into the frequency domain.